This invention relates to the field of processing multiple data signals to identify specific conditions in a process and, more particularly, the present invention relates to determining endpoints in plasma etch processing of semiconductors.
Commonly assigned U.S. Pat. No. 6,021,215 describes a data visualization method and system that is used in a manufacturing process, and more particularly, a semiconductor manufacturing process to determine plasma etch conditions. Sequences of sets of input data signals reflect the state of an observed process as state variables in a plasma etch process. Each set of input data signals is transformed using a Fourier-like transform and represented in polar coordinate form such that a visual display of the transformed set of signals appears as a xe2x80x9cblobxe2x80x9d. The sequence of sets of output data signals can then be displayed as a sequence of blobs. Based upon visually observable changes in the blob characteristics, the endpoints in the process can be determined. Thus, by observing changes in blob shapes, it is possible to visually determine that an endpoint to an etch process has occurred. However, it is not always desirable to use data visualization and blob analysis.
Among the several objects and features of the present invention may be noted the representation of many channels of information from currently available in-situ process signals in a single parameter in order to detect subtle changes indicating an endpoint to a process.
In accordance with the present invention, the method processes a sequence of sets of input data signals, each set of input data signals comprising mxe2x89xa72 data signals. Each set of input data signals is transformed to a set of output data signals based on an orthogonal polynomial transform function to generate a sequence of sets of output signals. The data signals are used as coefficients in evaluating the polynomial transform function. The transformed signals are integrated, based on the polynomial expansion, to determine an area as a function of time.
In still another aspect of the present invention, the method comprises the step of integrating between upper and lower limits. Each set of input data signals can reflect the state of an observed process. The sets of input data signals comprise data signals I1, I2, . . . Im, which reflect real time observations of respective state variables of the observed process. They can also reflect non-real time observation for the process.
In another aspect of the present invention, the state variables can represent intensity values at optical emission spectrum wavelengths that are monitored in the plasma etching process. They can also represent radio frequency power and DC bias. In another aspect of the present invention, the state variables represent process temperatures during the plasma etch process.
A system for processing a sequence of m-dimensional input data signals, with mxe2x89xa62, comprises a data processor for transforming each m-dimensional input data signal to an output transform signal based on an orthogonal polynomial transform function. These transform signals can be converted to a polar coordinate form to form respective blob signals for visual analysis as described in U.S. Pat. No. 6,021,215. However, it may be preferable to perform integration on the orthogonal transform function to obtain a set of scalar values that can be used to detect process endpoints by detection of amplitude changes.